A vaccine is a public health measure aimed at reducing disease spread through the population.
If you want kids to go to preschools, and not be little disease vectors transmitting infection between households, you should be looking for ways to avoid them acquiring the infection even if the disease has no ill effects on them personally.
Having their parents or grandparents hospitalized are also negative outcomes for a child.
I’m pretty sure we’re talking about public health measures that - if successful- will reduce covid risks for everyone.
And if we have to save the lives of a bunch of 90 year olds in order to also save the lives of some kids, we’ll that is a risk I am willing to take.